1. Field of the Invention
The invention relates to a method of manufacturing a magnet, and a magnet.
2. Description of Related Art
Neodymium magnets (Nd—Fe—B magnets) have been used as high performance magnets. However, dysprosium (Dy), which is expensive and rare, is used to manufacture high performance neodymium magnets. Therefore, development of magnets that are manufactured without using dysprosium has been promoted recently. Sm—Fe—N magnets that are manufactured without using dysprosium are known. However, because the decomposition temperature of a Sm—Fe—N compound is low, it is difficult to subject the Sm—Fe—N compound to high temperature sintering. If the Sm—Fe—N compound is sintered at a temperature equal to or higher than the decomposition temperature, the compound is decomposed. This may cause a possibility that the magnet will not be able to exhibit its performance as a magnet. Thus, material powders of the compound are bonded by a bonding agent. However, using the bonding agent causes a decrease in the density of the material powders, which may be a factor of a decrease in the residual magnetic flux density.
Japanese Patent Application Publication No. 2009-76755 describes that rare earth-transition metal alloy powders are sintered by being irradiated with microwaves in a vacuum atmosphere or an inert gas atmosphere.
It is not easy to manufacture a magnet by irradiating a compact made of powders of Sm—Fe—N compound with microwaves. If the compact is irradiated with microwaves, microwave heating occurs in an outer face side portion of the compact irradiated with the microwaves and therefore the powders in the outer face side portion attempt to be bonded together. However, if the powders in the outer face side portion of the compact are bonded together, an inside portion of the compact is not irradiated with the microwaves and therefore the powders in the inside portion of the compact are not bonded together. As a result, the bending strength of the magnet becomes low. Further, if the outer face side portion of the compact is continuously irradiated with the microwaves, the temperature of the outer face side portion of the compact is increased beyond the decomposing temperature, resulting in reduction of the performance of the magnet.